A battery is a known device used in storage and release of electric energy for various applications. In order to produce electric energy, a battery typically directly converts chemical energy into electric energy. Generally, a single battery includes one or more galvanic cells, where each cell is composed of two half cells electrically separated except for leading to an external circuit. During discharge, electrochemical reduction occurs in the cathode of the battery, and electrochemical oxidation occurs in the anode of the battery. While in the battery, the cathode and the anode are not in contact with each other physically, they are generally, chemically connected to each other by one or more ion-conductive and electrical electrothermal electrolytes, which may be in a solid state, a liquid state, or in a combination thereof. In case where an external circuit or load is connected to a terminal connected to an anode, and a terminal connected to a cathode, the battery drives electrons through an external circuit, and ions move through an electrolyte.
Batteries may be classified in various manners. For example, a battery completely discharged for one use is often referred to as a primary battery, or a primary cell. However, a battery discharged and rechargeable for more than one use is often referred to as a secondary battery or a secondary cell. The ability of a battery or a cell to be charged and discharged multiple times depends on the Faradaic efficiency of each charge and discharge cycle.
A sodium-based rechargeable battery includes various materials and designs, and many sodium batteries requiring a high Faradaic efficiency uses a solid primary electrolyte separator. A major advantage of using a solid ceramic primary electrolyte membrane is to achieve 100% of the Faradaic efficiency of the obtained battery. Actually, in most of other battery designs, a negative electrolyte solution and a positive electrolyte solution of the battery may be mixed with time, and thus, reduction of a Faradaic efficiency and loss of a battery capacity are induced.
A primary electrolyte separator used in a sodium battery requiring high Faradaic efficiency is often composed of an ion conductive polymer, an ion conductive liquid or gel-permeated porous material, or high-density ceramic. In this regard, most, but not all of the rechargeable sodium batteries which may be currently used for a commercial use include a molten sodium metal anode, a sodium β″-alumina ceramic electrolyte separator, and a molten cathode (which may include a composite of molten sulfur and carbon (referred to as a sodium/sulfur battery), molten NiCl2, NaCl, FeCl2 and/or NaAlCl4 (referred to as a ZEBRA battery)).
Despite the advantageous properties related to several typical sodium-based rechargeable batteries, such batteries may have significant disadvantages. In one example, since the sodium β″-alumina ceramic electrolyte separator may typically have higher conductivity, and is wetted well by molten sodium at a temperature above about 270° C., and/or typically a temperature above 300° C. is needed in order that sodium polysulfides remain in a molten state in a cathode, the battery undergoes significant thermal management and heat-sealing problems. For example, some sodium-based rechargeable batteries may have difficulties in removing heat from the batteries or maintaining the anodes and cathodes at relatively high operating temperature.
In another example, some sodium-based batteries may cause a significant safety problem, due to their relatively high operating temperature.
In another example, some sodium-based batteries require a battery component capable of being operated at a high temperature. Therefore, such component may be relatively expensive.
In another example, since a relatively large amount of energy may be needed in order to heat some general sodium-based batteries to a relatively high operating temperature, such a battery may require much money to be operated, while still being energy inefficient.
That is, in the case of the existing sodium-based secondary battery such as a sodium-sulfur battery or a sodium-nickel chloride battery, conductivity and a melting point of battery components should be considered.
The sodium-nickel chloride battery should be operated at least at 250° C., and the sodium-sulfur battery has an operating temperature of at least 300° C.
Due to such problems, those batteries are very disadvantageous in an economic aspect in view of manufacturing or operation for reinforcement of temperature maintenance, sealability maintenance and safety.